This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goal of our overall project is to develop 129-Xe MRI biosensors for early cancer detection and possible therapeutic intervention. We are currently synthesizing cryptophanes and other carriers that will have greater affinity for xenon, longer 129Xe hyperpolarized spin-lattice relaxation times, and unique chemical shifts. Cryptophane-A, an organic cage compound, binds xenon (Xe) in its internal cavity with the highest affinity of any known molecule and fluoresces with a maximum intensity around 314nm. The presence of excess Xe in aqueous solution with the cryptophane quenches the observed fluorescence with an efficiency of about 50% as measured by steady-state experiments. This quenching is believed to be largely static in nature, a result of the bound Xe atom residing very close to the veratole chromophores of the cryptophane. Fluorescence lifetime measurements would allow for the determination of the biomolecular quenching constant or a confirmation of the static quenching process.